The invention relates to a structural member, particularly for paneling or construction purposes. The invention also relates to a method for producing such a structural member and its use. The invention also relates to a tool for producing the structural member.
The use of layered components (sandwich components), for example as paneling or structural elements, is known in lightweight construction. A layered component, e.g. for self-supporting bodies, consists of a stack structure with two cover layers between which a core material (a core layer) is located. These layers are designed so that the weight of the component is as low as possible, yet has as high a load-bearing capacity as possible. A material with a high modulus of elasticity, e.g. fiber-reinforced plastic, is therefore selected for the cover layers, whilst a less rigid but as light as possible a material is used for the core layer. Hitherto, the core layer has frequently been made of foam or honeycomb materials in practice. Conventional honeycomb materials typically consist of cells, the side walls of which forming the characteristic comb with a hexagonal basis area (honeycomb).
Due to their low rigidity, relatively high density and high flammability, the foam materials have a series of disadvantages. In contrast, honeycomb materials have a better rigidity-to-weight ratio and lower flammability. Nevertheless, conventional honeycomb materials are subject to restrictions in lightweight construction, due to the following disadvantages.
A first disadvantage is the complicated method for producing the cells of the honeycomb material. For, example, a conventional method consists of first gluing paper plies by means of paper webs, then drawing them apart and finally soaking them with a phenol resin and allowing it to cure. Slices cut from these paper honeycombs can then be used as core layers in lightweight construction. All the phases of this method must be carried out with great precision, to produce uniform and stable core layers. This requires complicated, expensive precision machinery. In other conventional techniques (see e.g. WO 00/58080 and WO 00/32382), the cells are formed by the deformation of so-called folded combs. These methods are also disadvantageous, due to the high demands for precision and the associated high production costs.
A further disadvantage of conventional honeycomb materials is the anisotropy of the rigidity characteristics. As the cells are formed by gluing folded paper strips together, each cell has walls consisting of a double layer of paper in certain directions and walls with a single layer of paper in other directions, so that the rigidity of the honeycomb material is differently influenced in the various directions.
Finally, conventional honeycomb materials present the disadvantage of restricted freedom of design in adaptation for a specific use. For example, a honeycomb core layer cannot be stiffened locally at certain points without further measures. Stiffening has hitherto only been achieved with core filling materials, which, however, entail weight problems. In addition, curved sandwich structures which use the honeycomb as a core material can only be produced either by cutting the honeycomb used to the curves required or by adapting it to the curve by applying force in the form of pressure (the “crushed core” method), which destroys the honeycomb.
Planar structures, which are formed by deep-drawing a plastic material and distinguished by a base layer with tapered stump-shaped elevations (see e.g. DE 197 21 370, EP 411 372, EP 512 431) represent an alternative to honeycomb materials. The use of such planar structures has been proposed for lightweight construction (EP 158 234, EP 250 005), automotive construction (EP 409 120) and also for other functional elements (EP 725 454). However, these planar structures have the disadvantage of relatively low compressive rigidity, so that lightweight structural members which are made using them have a pronounced tendency to deformation.
Lightweight structural members are known from U.S. Pat. No. 5,683,782 and U.S. Pat. No. 5,032,208, in which the core layers are formed by a plurality of cylindrical tubular sections, the outer sides of which are interconnected. The production process of these lightweight structural members, in which the core layers are cut from stacks of tubes glued together by their outer sides, and the restricted versatility in adapting lightweight structural members to a specific task, are particularly disadvantageous.
The objective of the invention is to provide an improved structural member, particularly for lightweight construction, which can overcome the disadvantages of conventional core layer materials and which is characterized by high rigidity. It should also be possible to produce the structural member with simple resources and it should have a high degree of freedom of design in adaptation to the respective application. The objective of the invention is also to provide an improved method of producing a structural member for lightweight construction.
These objectives are solved by a structural member and a method with the features of the invention. Advantageous embodiments and applications of the invention are defined below.